As a bearing in a transmission system of a car, for example, a closed rolling bearing is used. As this closed rolling bearing, for example, a structure is known in which multiple rolling elements are arranged between an inner ring raceway and an outer ring raceway, a seal groove is formed at both sides of the inner ring raceway in a circumferential direction, and a locking groove is formed, in the circumferential direction, at both sides of an inner circumferential surface of the outer ring raceway facing the seal groove, wherein a circular rubber seal is put in the locking groove, and a sealing lip of the tip of the rubber seal is arranged so that it is in sliding contact with a side wall of the seal groove (see Patent Documents 1 and 2). The sliding-contact arrangement of the sealing lip, as described above, can prevent both leakage of a lubricant in the bearing and contamination from the outside.
In reaction to recent, increased desire for reduction of environmental burdens and lower fuel consumption, a running torque of the bearing used in the transmission system of a car is required to be lower than that of conventional bearings, and also as the rubber seal put in the bearing, a rubber seal capable of providing a lower torque is required accordingly.
In order to respond to such a requirement for obtaining a lower torque, it can be considered to adopt a method for reducing a running torque by contriving the shape of the sealing lip thereby reducing the rigidity, or a method for reducing a running torque by decreasing a jamming of the rubber seal. According to these methods, however, a shape of the sealing lip is limited and sizes of the seal vary, and the operation and maintenance are problematically difficult, taking account of assembly.
It is proposed to use a rubber seal reducing a running torque due to decrease of a jamming caused by an initial abrasion of the sealing lip while it is slid in an early stage of rotation (see Patent Document 3).